USE OF COMPOUNDS IN POLYMERISATION REACTIONS

Abstract

A use of ansa-metallocene complexes for the polymerisation of cyclic esters and cyclic amides is disclosed. The ansa-metallocene complexes are particularly active as initiators/catalysts in the polymerisation of lactides, with the resulting polymeric material demonstrating low polydispersity.

Claims

1. A polymerization process comprising contacting one or more of a cyclic ester or a cyclic amide with a compound according to formula I: ##STR00020## wherein: R.sub.1 and R.sub.2 are each independently (1-2C)alkyl; R.sub.3 and R.sub.4 are each independently hydrogen or (1-4C)alkyl, or R.sub.3 and R.sub.4 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl].sub.2amino and S(O).sub.2(1-6C)alkyl; R.sub.5 and R.sub.6 are each independently hydrogen or (1-4C)alkyl, or R.sub.5 and R.sub.6 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl].sub.2amino and S(O).sub.2(1-6C)alkyl; R.sub.a and R.sub.b are independently selected from (1-6C)alkyl, (1-6C)alkoxy, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkylamino, [(1-6C)alkyl].sub.2amino, aryl, halo, amino, nitro and cyano; X is selected from zirconium or hafnium; and each Y group is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, halo, nitro, amino, phenyl, (1-6C)alkoxy, C(O)NR.sub.xR.sub.y, or Si[(1-4C)alkyl].sub.3; and wherein R.sub.x and R.sub.y are independently (1-4C)alkyl.

2. The process of claim 1, wherein R.sub.3 and R.sub.4 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and halo.

3. The process of claim 1, wherein R.sub.3 and R.sub.4 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or heteroaryl, wherein each aryl or heteroaryl group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and halo.

4. The process of claim 1, wherein R.sub.3 and R.sub.4 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, aryl or heteroaryl, wherein each aryl or heteroaryl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy and halo.

5. The process of claim 1, wherein R.sub.3 and R.sub.4 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring.

6. The process of claim 5, wherein R.sub.3 and R.sub.4 are each hydrogen.

7. The process of claim 1, wherein R.sub.5 and R.sub.6 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and halo.

8. The process of claim 1, wherein R.sub.5 and R.sub.6 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or heteroaryl, wherein each aryl or heteroaryl group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and halo.

9. The process of claim 1, wherein R.sub.5 and R.sub.6 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, aryl or heteroaryl, wherein each aryl or heteroaryl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy and halo.

10. The process of claim 9, wherein R.sub.5 and R.sub.6 are each independently hydrogen or linear (1-4C)alkyl, or R.sub.1 and R.sub.2 are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring.

11. The process of claim 1, wherein R.sub.5 and R.sub.6 are each hydrogen.

12. The process of claim 1, wherein X is Zr.

13. The process of claim 1, wherein each Y is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from halo and (1-4C)alkyl.

14. The process of claim 1, wherein each Y is independently selected from halo, hydride, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from halo and (1-4C)alkyl.

15. The process of claim 1, wherein each Y is independently selected from halo, or a (1-6C)alkoxy, or aryloxy group which is optionally substituted with one or more groups selected from halo and (1-4C)alkyl.

16. The process of claim 1, wherein each Y is independently selected from Cl, Br, I or a group OR.sub.7, wherein R.sub.7 is a phenyl group optionally substituted with one or more R.sub.8, wherein each R.sub.8 is independently (1-4C)alkyl.

17. The process of claim 1, wherein R.sub.1 and R.sub.2 are each independently (1-2C)alkyl.

18. The process of claim 17, wherein R.sub.1 and R.sub.2 are each methyl.

19. The process of claim 1, wherein R.sub.a and R.sub.b are each independently (1-6C)alkyl or (2-6C)alkenyl.

20. The process of claim 19, wherein R.sub.a and R.sub.b are each independently (1-4C)alkyl.

21. The process of claim 20, wherein R.sub.a and R.sub.b are each methyl.

22. The process of claim 1, further comprising an activator.

23. The process of claim 22, wherein the activator is an alcohol

24. The process of claim 23, wherein the activator is tert-butanol, benzyl alcohol or iso-propanol

25. The process of claim 1, wherein the one or more cyclic amide or cyclic ester is selected from a lactide or a lactam.

26.-27. (canceled)

Description

EXAMPLES

[0123] Particular examples of the invention will now be described, for illustrative purposes only. with references to the accompanying figures, in which:

[0124] FIG. 1 shows polymerisation plots of lactide conversion in function of time using SB(Cp,I*)ZrCl.sub.2 (square), SB(Cp,I*)HfCl.sub.2 (circle) and SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.6H.sub.3) (triangle). Data points are an average of the results for each temperature.

[0125] FIG. 2 shows MALDI-TOF mass spectrum of PLA produced from SB(Cp,I*)ZrCl.sub.2 and (S,S)-LA. Polymerisation conditions: 80 C., [LA].sub.0:[SB(Cp,I*)ZrCl.sub.2] of 20:1, [LA].sub.0=0.5 M, d.sub.1-chloroform.

[0126] FIG. 3 shows Polymerisation plots of lactide conversion in function of time using SB(Cp,I*)ZrCl.sub.2 (square), SB(Cp,I*)HfCl.sub.2 (circle) and SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.6H.sub.3) (triangle). Data points are an average of the results for each temperature.

[0127] FIG. 4 shows an Eyring-Polanyi plot for the polymerisation of (S,S)-lactide with SB(Cp,I*)ZrCl.sub.2. Data points are an average of the results for each temperature, error bars are calculated to one standard deviation.

[0128] FIG. 5 shows a double logarithmic plot of variation of concentration of SB(Cp,I*)ZrCl.sub.2 with k.sub.obs for (S,S)-lactide.

Example 1a

Synthesis of SB(Cp,I*)ZrCl.SUB.2

[0129] ##STR00017##

[0130] Toluene (40 ml) was added to a LiCp (246 mg, 3.41 mmol) and Ind*SiMe.sub.2Cl (1 g, 3.41 mmol) in a Schlenk tube, dissolved in 5 C. THF (50 mL) and left to stir for two hours. .sup.nBuLi (4.7 mL, 1.6 M in hexanes, 7.51 mmol) was added, dropwise, over 30 minutes and the reaction left to stir for 12 hours. The solvent was removed in vacuo and the residue washed with pentane (340 mL) and dried to afford a grey powder. One equivalent of ZrCl.sub.4 (796 mg, 3.41 mmol) was added and the mixture dissolved in benzene and left to stir for sixty hours. The solution changed colour from green, to orange and finally red/brown. The solvent was removed under vacuum and the product extracted with pentane (340 mL) and filtered through Celite. The filtrate was concentrated in vacuo and stored at 34 C. This yielded SB(Cp,I*)ZrCl.sub.2 as an orange/brown precipitate in 23% yield (365 mg, 0.76 mmol). Orange crystals, suitable for single crystal X-ray diffraction, were grown from a concentrated solution in hexanes at 34 C.

[0131] .sup.1H NMR (d.sub.6-benzene): 6.59 (2H, dm, CpH), 5.60 (2H, dm, CpH), 2.52 (3H, s, ArMe), 2.48 (3H, s, ArMe), 2.26 (3H, s, ArMe), 2.15 (3H, s, ArMe), 2.05 (3H, s, ArMe), 1.97 (3H, s, ArMe), 0.72 (3H, s, SiMe), 0.64 (3H, s, SiMe).

[0132] .sup.13C{.sup.1H} NMR (d.sub.6-benzene): 135.65 (Ar), 135.13 (Ar), 134.86 (Ar), 131.11 (Ar), 131.50 (Ar), 131.15 (Ar), 129.16 (Ar), 126.35 (Ar), 125.92 (ArSi), 115.87 (CpH), 106.49 (CpH), 84.01 (CpSi), 21.69 (ArMe), 17.91 (ArMe), 17.64 (ArMe), 17.16 (ArMe), 16.92 (ArMe), 15.97 (ArMe), 5.59 (SiMe), 3.26 (SiMe).

[0133] MS (EI): Predicted: m/z 482.0372. Observed: m/z 482.0371.IR (KBr) (cm.sup.1): 2961, 2925, 1543, 1260, 1029, 809, 668.

[0134] CHN Analysis (%): Expected: C 54.74, H 5.85, Found: C 54.85, H 5.94.

Example 1b

Synthesis of SB(Cp,I*)HfCl.SUB.2

[0135] ##STR00018##

[0136] SB(Cp,I*)Li.sub.2 (1 g, 2.99 mmol) and HfCl.sub.4 (958 mg, 2.99 mmol) were added to a Schlenk tube. Benzene (100 mL) was added and the reaction was left to stir for 60 hours. The solution changed colour from brown to yellow. The solvent was the removed under vacuum and the product was extracted with pentane (340 mL) and filtered through Celite. The filtrate was concentrated in vacuo and stored at 34 C. yielding SB(Cp,I*)HfCl.sub.2 as yellow crystals, suitable for single crystal X-ray diffraction, in 24% yield (360 mg, 0.632 mmol).

[0137] .sup.1H NMR (d.sub.6-benzene): 6.54 (3H, dm, CpH), 5.53 (3H, dm, CpH), 2.57 (3H, s, ArMe), 2.56 (3H, s, ArMe), 2.25 (3H, s, ArMe), 2.20 (3H, s, ArMe), 2.09 (3H, s, ArMe), 2.03 (3H, s, ArMe), 0.65 (3H, s, SiMe), 0.57 (3H, s, SiMe).

[0138] .sup.13C{.sup.1H} NMR (d.sub.6-benzene): 134.55 (Ar), 134.18 (Ar), 133.51 (Ar), 131.73 (Ar), 131.05 (Ar), 129.64 (Ar), 126.23 (Ar), 125.18 (Ar), 124.38 (Ar), 113.33 (C.sub.pH), 107.32 (C.sub.pH), 82.33 (C.sub.pSi), 21.53 (ArMe), 17.68 (ArMe), 17.37 (ArMe), 16.77 (ArMe), 16.64 (ArMe), 15.51 (ArMe), 5.00 (SiMe), 3.00 (SiMe).

[0139] MS (EI): Predicted: m/z 570.0785. Observed: m/z 570.0701. IR (KBr) (cm.sup.1): 2960, 2923, 1542, 1262, 1028, 812, 670.

[0140] CHN Analysis (%): Expected: C 46.36, H 4.95, Found: C 46.52, H 5.04.

Example 1c

Synthesis of SB(Cp,I*)ZrCl(O-Me.SUB.2.-C.SUB.6.H.SUB.3.)

[0141] ##STR00019##

[0142] SB(Cp,I*)ZrCl.sub.2 (100 mg, 0.207 mmol) and 2,6-dimethyl potassium phenoxide (66 mg, 0.414 mmol) were added to a Schlenk tube, dissolved in benzene (20 mL), and left to stir for sixteen hours. The solvent was removed in vacuo and the product extracted with pentane (220 mL). The .sup.1H NMR spectra showed resonances corresponding to a mixture of two isomers. Thin, yellow crystals of isomer (a), suitable for single crystal X-ray diffraction were obtained when the solution was concentrated and stored in a 34 C. freezer. Purity was 94% by .sup.1H NMR spectroscopy and crystals were obtained in 15% yield (16 mg, 0.028 mmol).

[0143] Isomer (a):

[0144] .sup.1H NMR (d.sub.6-benzene): 7.06 (2H, dd, Ar.sub.phenH), 6.82 (1H, t, Ar.sub.phenH), 6.26 (1H, m, CpH), 6.13 (1H, m, CpH), 5.93 (1H, m, CpH), 5.61 (1H, m, CpH), 2.34 (3H, s, ArMe), 2.24 (3H, s, ArMe), 2.22 (6H, s, Ar.sub.phenMe), 2.19 (3H, s, ArMe), 2.18 (3H, s, ArMe), 2.15 (3H, s, ArMe), 1.99 (3H, s, ArMe), 0.81 (3H, s, SiMe), 0.75 (3H, s, SiMe).

[0145] Isomer (b):

[0146] .sup.1H NMR (d.sub.6-benzene): 6.88 (2H, dd, Ar.sub.phenH), 6.69 (1H, t, Ar.sub.phenH), 6.51 (1H, m, CpH), 6.02 (1H, m, CpH), 5.88 (1H, m, CpH), 5.80 (1H, m, CpH), 2.61 (3H, s, ArMe), 2.42 (6H, s, Ar.sub.phenMe), 2.40 (3H, s, ArMe), 2.08 (3H, s, ArMe), 1.99 (3H, s, ArMe), 1.64 (3H, s, ArMe), 1.48 (3H, s, ArMe), 0.64 (3H, s, SiMe), 0.61 (3H, s, SiMe).

Example 2

Lactide Polymerisation

[0147] Polymerisations were carried out in Young's tap NMR tubes containing 40 mg, 0.278 mmol of either L-lactide or rac-lactide in a d.sub.1-chloroform solution with an amount of initiator to correspond to an initiator/lactide ratio of 50:1. The reaction was followed by .sup.1H NMR spectroscopy comparing the integration values of the methine signals of PLA and LA. All polymerisations were worked up by decanting into 5 C. pentane (10 mL), removing the pentane, washing the resultant polymer with diethyl ether (10 mL) and drying under vacuum for 18 hours.

[0148] Polymerisation studies were carried out using SB(Cp,I*)ZrCl.sub.2 and SB(Cp,I*)HfCl.sub.2 in the presence of two equivalents of benzyl alcohol as a co-initiator, which is postulated to form the bis(benzyl alkoxide) in situ and a mixture of mono(alkoxide) complexes SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.6H.sub.3) without a co-initiator.

[0149] In order to compare the activities of these complexes, all initial polymerisation studies were carried out at 80 C. in d.sub.1-chloroform, with an S,S-LA: initiator ratio of 50:1, ensuring that [S,S-LA]=0.5 M.

TABLE-US-00001 TABLE 1 Rate constants and GPC data for ring-opening polymerisation of S,S-LA with selected initiators. Initiator k.sub.obs (h.sup.1) M.sub.n,exp (gmol.sup.1) PDI (M.sub.w/M.sub.n) SB(Cp,I*)ZrCl.sub.2 0.2317 4071 1.10 SB(Cp,I*)HfCl.sub.2 0.2262 3826 1.11 SB(Cp,I*)ZrCl(OR) 0.2081 18032 1.30 R = 2,6-Me.sub.2C.sub.6H.sub.3

[0150] The results shown in Table 1 and FIG. 1 demonstrate that SB(Cp,I*)ZrCl.sub.2 displays the highest activity with 88% conversion in seven hours (k.sub.obs=0.23170.0058 h.sup.1), closely followed by SB(Cp,I*)HfCl.sub.2 with 81% conversion in six hours (k.sub.obs=0.22620.0147 h.sup.1) while SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.6H.sub.3) was slower with 66% conversion in 5 hours (k.sub.obs=0.20810.0055 h.sup.1). The values of 1.10 and 1.11 for SB(Cp,I*)ZrCl.sub.2 and SB(Cp,I*)HfCl.sub.2 show that polymerisation is well controlled for these. The value reported for SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.6H.sub.3) is slightly higher but is still considered controlled; the higher value could be attributed to the mixture of isomers used in the polymerisation.

[0151] The MALDI-TOF mass spectrum of the polymer produced when (S,S)-LA was polymerised with SB(Cp,I*)ZrCl.sub.2 and benzyl alcohol shows a series of peaks which are m/z=72 apart (FIG. 2).

[0152] FIG. 3 shows a plot of In([LA].sub.0/[LA].sub.t) against time using SB(Cp,I*)ZrCl.sub.2 and SB(Cp,I*)ZrCl.sub.2 with 2 equivalents of benzyl alcohol, and SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.3H.sub.6) in the absence of a co-initiator, at 80 C. with an initial rac-lactide concentration of 0.5 M.

TABLE-US-00002 TABLE 2 Rate constants and GPC data for ring opening polymerisation of rac-LA with selected initiators. Initiator k.sub.obs (h.sup.1) M.sub.n,exp (gmol.sup.1) PDI (M.sub.w/M.sub.n) SB(Cp,I*)ZrCl.sub.2 0.3948 17826 1.07 SB(Cp,I*)HfCl.sub.2 0.0258 SB(Cp,I*)ZrCl(OR) 0.2617 15981 1.18 R = 2,6-Me.sub.2C.sub.6H.sub.3

[0153] Table 2 shows that SB(Cp,I*)ZrCl.sub.2 catalyses rac-LA the fastest, k.sub.obs=0.3948 h.sup.1, shortly followed by SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.3H.sub.6), k.sub.obs=0.2617 h.sup.1. The PDI value of 1.07 for SB(Cp,I*)ZrCl.sub.2 is very low when compared with literature. SB(Cp,I*)ZrCl(O-2,6-Me.sub.2-C.sub.3H.sub.6) shows slightly less control, compared to SB(Cp,I*)ZrCl.sub.2 and SB(Cp,I*)HfCl.sub.2, over the molecular weight with a PDI of 1.18 (which is still considered controlled).

[0154] The effect of temperature on the rate constant and GPC data for ring-opening polymerisation of S,S-Lactide with SB(Cp,I*)ZrCl.sub.2 was also investigated. The results are outlined in Table 3 below:

TABLE-US-00003 TABLE 3 Rate constants and GPC data for ring-opening polymerisation of S,S- Lactide with SB(Cp,I*)ZrCl.sub.2 at variable temperatures initiators. Temp/ C. k.sub.obs/h.sup.1 M.sub.n, exp/gmol.sup.1 PDI (M.sub.w/M.sub.n) 60 0.0731 70 0.1252 3190 1.08 80 0.2317 3870 1.11 90 0.3033 5046 1.13

[0155] A plot of In(k.sub.obs/T) against 1/T (FIG. 4) gives a linear plot with gradient of H.sup./R and an intercept of S.sup./R+In(k.sub.B/h). The lactide: initiator ratio was kept at 50:1 maintaining an initial (S,S)-lactide concentration of 0.5 M. The value of H.sup. obtained from this study is 494 kJmol.sup.1, the value obtained for S.sup. was 1889 Jmol.sup.1K.sup.1 again this is well within the values in the literature, with the negative sign indicating the transition state has a higher degree of order than the starting material, as is to be expected for a coordination-insertion mechanism.

[0156] A further study was undertaken to investigate how the zirconium concentration affected the overall polymerisation rate. A constant concentration of 0.5 M of (S,S)-lactide was used and lactide:initiator ratios of 10:1, 25:1, 50:1 and 100:1 were used ([Zr]=0.05, 0.02, 0.01 and 0.005 M respectively).

[0157] The double logarithmic plot of In[Zr] against In[k.sub.obs] (FIG. 5) reveals a straight line plot with slope of 0.9. As expected for a first order rate law the rate, k.sub.obs, increases with increasing initiator concentration as there are more active species present to polymerise the monomer.

[0158] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.