Photoinitiators for polyolefins

Abstract

The technology disclosed herein concerns a family of alkoxybenzophenones for use as photoinitiators for crosslinking polyolefins.

Claims

1. A photoinitiator for use in a method of crosslinking at least one polyolefin, wherein the photoinitiator is an alkoxybenzophenone of the general Formula (I): ##STR00002## wherein (i) R.sub.1 is —O—(CH.sub.2).sub.n—(C═O)—O—(CH.sub.2).sub.m—CH.sub.3, wherein for each variant, independently, each of n and m, independently of the other, is between 0 and 3; R.sub.2 is H, —(CH.sub.2).sub.n—CH.sub.3 or —O—(CH.sub.2).sub.n—CH.sub.3, wherein for each variant, independently, each n is an integer between 4 and 15; and R.sub.3 is H, —(CH.sub.2).sub.n—CH.sub.3, —O—(CH.sub.2).sub.n—CH.sub.3 or —O—(C═O)—(CH.sub.2).sub.m—CH.sub.3, wherein for each variant, independently, each of n and m, independently of the other, is an integer between 4 and 15; or (ii) R.sub.1 is —O—(CH.sub.2).sub.n—CH.sub.3 wherein n is between 1 and 3, or —O—(CH.sub.2).sub.n(C═O)—O—(CH.sub.2).sub.m—CH.sub.3, wherein of n and m, independently of the other, is between 0 and 3; R.sub.2 is —H, —(CH.sub.2).sub.n—CH.sub.3 or —O—(CH.sub.2).sub.n—CH.sub.3, wherein for each variant, independently, each n is an integer between 4 and 15; and R.sub.3 is —H, —(CH.sub.2).sub.n—CH.sub.3, —O—(CH.sub.2).sub.n—CH.sub.3 or —O—(C═O)—(CH.sub.2).sub.m—CH.sub.3, wherein for each variant, independently, each of n and m, independently of the other, is an integer between 4 and 15; or (iii) R.sub.1 is —O—(CH.sub.2).sub.nCH.sub.3 or —O—(CH.sub.2).sub.n—(C═O)—O—(CH.sub.2).sub.m—CH.sub.3, wherein for each variant, independently, each of n and m, independently of the other, is between 0 and 3; R.sub.2 is —H, —(CH.sub.2).sub.n—CH.sub.3 or —O—(CH.sub.2).sub.n—CH.sub.3, wherein for each variant, independently, each n is an integer between 4 and 15; and R.sub.3 is —H, —(CH.sub.2).sub.n—CH.sub.3, —O—(CH.sub.2).sub.n—CH.sub.3 or —O—(C═O)—(CH.sub.2).sub.m—CH.sub.3, wherein for each variant, independently, each of n and m, independently of the other, is an integer between 4 and 15; provided that when R.sub.1 is —O—CH.sub.3, at least one of R.sub.2 and R.sub.3 is different from H.

2. The photoinitiator according to claim 1, wherein R.sub.1 is —O—CH.sub.2—CH.sub.3.

3. The photoinitiator according to claim 1, wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3.

4. The photoinitiator according to claim 1, wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H.

5. A compound of Formula (I): ##STR00003## the compound being selected from: a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; and a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H.

6. The compound according to claim 5, being: a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.7—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.9—CH.sub.3 and R.sub.3 is H; or a compound wherein R.sub.1 is —O—CH.sub.2—(C═O)—O—CH.sub.2—CH.sub.3, R.sub.2 is —O—(CH.sub.2).sub.11—CH.sub.3 and R.sub.3 is H.

7. The compound according to claim 5, wherein the compound is for use as a photoinitiator.

8. A photoinitiator being a compound according to claim 5.

9. A composition comprising at least one compound according claim 5, and optionally at least one polyolefin.

10. The composition according to claim 9, further comprising at least one promoter.

11. The composition according to claim 9, comprising at least one olefin and at least one promoter.

12. The composition according to claim 10, wherein the at least one promoter is selected from trimethylol propane tri-methacrylate (TMPTMA) and triallylisocyanurate (TAIC).

13. The composition according to claim 10, comprising between 0.5 and 5 wt % promoter.

14. The composition according to claim 9, comprising at least one photoinitiator at a concentration of between 0.01 and 10 wt %.

15. The composition according to claim 14, wherein the at least one photoinitiator is at a concentration of between 0.05 and 5 wt %.

16. A master batch comprising at least one photoinitiator according to claim 5, and optionally at least one promoter.

17. A method of crosslinking at least one polyolefin, the method comprising treating, under irradiation, said at least one polyolefin with an amount of a photoinitiator according to claim 5.

18. The method according to claim 17, wherein the polyolefin is selected from polyethylene and ethylene copolymers, polyethylene (PE), polypropylene, low density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), ultra-low-density polyethylene (ULDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), ultra-high-density polyethylene (UHDPE), ethylene/propylene copolymers, polypropylene (PP), propylene/ethylene copolymer, ethylene and ethylene, alcohol copolymer (EVOH), ethylene and propylene copolymer, polyisoprene, polybutylene, polybutene, poly-3-methylbutene-1, poly-4-methylpentene-1, or copolymers of ethylene with one or more alpha-olefins.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

(1) High efficacy photo-curing can be provided only in case photoinitiator and polymer possess high compatibility, namely both polyolefin or co-polymer and photoinitiator of the invention have to have similar values of Hansen solubility parameters. More specifically, the vector differences in polar, dispersive and hydrogen bonds components of Hansen solubility parameters (δ.sub.p, δ.sub.d, δ.sub.h) are to be less than 6.0 (J/cm.sup.3).sup.1/2.

(2) High solubility of photoinitiators of the invention accounts for interaction of exited state of photoirradiated benzophenone derivative (Norrish II mechanism of radical initialization) and a polymer molecule on the molecular level, to increase substantially transfer of energy from the photoinitiator to the polymer molecule, followed by formation of an alkyl radical by destruction of a C—H bond of the polyolefin or the co-polymer.

(3) In the Table 1 below, the Hansen solubility parameters for pure benzophenone photoinitiators and polyethylene are presented.

(4) TABLE-US-00001 TABLE 1 Solubility parameters of benzophenone and polyethylene Solubility parameters (J/cm.sup.3).sup.1/2 δ.sub.d δ.sub.p δ.sub.h Polyethylene 17.6 0 0 Benzophenone 19.5 7.2 5.1

(5) The vector difference of the solubility parameters is 9 (J/cm.sup.3).sup.1/2. This is more than the solubility limit of 6 (J/cm.sup.3).sup.1/2. As a result, benzophenone bloom out of polyethylene without any substantive photocuring after irradiation of a polyethylene composition containing an amount of the pure benzophenone.

(6) Photoinitiators of the invention possesses satisfactory solubility on polyethylene starting.

(7) In Table 2, data on solubility parameters of benzophenone derivative according to general Formula (II) the invention are presented.

(8) TABLE-US-00002 TABLE 2 Solubility parameters of benzophenone derivatives according to the invention. Photoinitiator type Solubility parameters (J/cm.sup.3).sup.1/2 δ.sub.d δ.sub.p δ.sub.h 1* R.sub.1 = —O—CH.sub.2—CH.sub.3, 18.8 4.5 3.0 R.sub.2: —O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 2** R.sub.1 = —O—CH.sub.2—CO—O—CH.sub.2—CH.sub.3, 19.0 4.8 3.2 R.sub.2 = —O—(CH.sub.2).sub.7—CH.sub.3 *Photoinitiator of type 1 can be easily synthesized using well known UV-absorber Chimassorb 81 (CAS# 1843-05-6) with BrCH.sub.2—CH.sub.3. **Photoinitiator of type 2 can be obtained from the same UV-absorber by reaction with ethyl ester of chloro-acetic acid.

(9) For the first benzophenone derivative in Table 2, the vector difference with solubility parameter of polyethylene is 5.5 (J/cm.sup.3).sup.1/2 and for the second derivative that difference is 5.9 (J/cm.sup.3).sup.1/2. That means that both benzophenone derivatives have a solubility parameter which is smaller than 6.0 (J/cm.sup.3).sup.1/2 and as such both exhibit solubility in polyethylene.

(10) Introduction of either photoinitiators of Table 2 in LDPE up to 5% w/w did not lead to any appreciable blooming effect which could have resulted from migration of the photoinitiator out of polymer matrix.

(11) In the below Examples, the efficiency of photo-induced cross-linking of photoinitiators according to the invention is presented with different polyolefins.

(12) Photoinitiators different from those of the invention, yet having a comparable compatibility with polyolefins were used as comparative examples. These were 4-octyloxybenzophenone, CAS #1843-05-6, 1- and 4-hydroxybenzophenone laurate, CAS #35820-92-9 listed in Table 2 above.

(13) It is well known that direct introduction of additives into polymers, as powders or liquids, leads to inhomogeneous distribution followed by non-even cross-linking Thus, before final mixing with polyolefins, master batches of particular photoinitiators were prepared. Concentration of the photoinitiator in the master batches was 10% w/w. Master batches were produced by a twin screw extruder with construction of screws providing very homogeneous distribution of the photoinitiators in the master batch. Adding master batches into virgin polyethylene following this procedure, and photo-irradiating the composition, resulted in reproducible results.

(14) Two types of experiments utilizing photoinitiators of the invention are presented in the examples below: Cross-linking films made of LDPE in a single bubble extrusion process in order to improve tensile properties of films (e.g. for packaging), while keeping UV-treated polymer in a form capable of melt welding; Cross-linking of LLDPE primary tube of oriented films made by a double bubble technology, in order to increase tensile properties of the melt during orientation of first bubble by inflation (stretching).

(15) In the case of the film of the first type above, a LDPE film was UV-irradiated off line. Irradiation of the film was conducted from both sides.

(16) In case of the oriented film, production UV-sources were placed on both sides of a primary tube before orientation. UV-treatment was performed on line.

(17) For both types of films, efficiency of cross-linking was tested by measuring creep of film (1.0 inch width) at 135° C. with a loading weight of between 50 g and 57 g.

(18) 1.0 mm, 2.0 mm and 3.0 mm thick slabs of different polyolefins (LDPE, HDPE) were prepared by a method of melt pressing to simulate cables insulating coatings or pipes. Master batches of cross-linking promoters [e.g., trimethylol propane tri-methacrylate (TMPTMA) and Triallylisocyanurate (TAIC)] were added as master batches containing between 5 and 25% of the cross-linking promoter. Efficiency of used UV-initiators was tested by measurement of gel fraction in the irradiated polymer by extraction of sol fraction by boiled Xylene.

(19) Slabs were irradiated with UV-light from a UV-lamp and conveyer.

(20) Power of the UV-lamps used was 1.0 kW. Appropriate equipment was used to measure exposure dose in J/cm.sup.2.

(21) Table 3 presents data on exposure dose needed to cross-link samples to get creep time of 15 sec for acquiring desired tensile properties.

(22) TABLE-US-00003 TABLE 3 Exposure dose in J/cm.sup.2 to obtain creep time for irradiated LDPE films 30 micron thick containing photoinitiators according to Formula (II) and for comparative photoinitiators. Concentration of Exposure Dose*, Number Sample name photo-initiator, % J/cm.sup.2 1 According to Formula (I), 0.3 3.5 R.sub.1 = —O—CH.sub.2—CH.sub.3, R.sub.2 = O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 2 According to Formula (I), 0.25 3.0 R.sub.1 = —O—CH.sub.2—CO—O—CH.sub.2—CH.sub.3, R.sub.2 = —O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 3 4-octyloxybenzophenone, 0.35 4.6 CAS#1843-05-6 (comparative) 4 4-hydroxybenzophenone laurate, 0.35 4.8 CAS#35820-92-9, (Comparative) *Exposure dose of UV-irradiation to get 15 sec creep time, 135 C., 57 g load

(23) As may be noted from Table 3, photoinitiators of Formula (I) and (II) proved to be substantially effective in photo-cross-linking LDPE, as compared to the comparative photoinitiators. For the comparative photoinitiators, the concentrations must be higher in order to achieve crosslinking to achieve a 15 sec creep time

(24) In Table 4, data are presented on the exposure dose needed to obtain 15 sec creep time for oriented LLDPE films, 20 micron thick in case of on line UV-irradiation of primary tube of 0.4 mm thick.

(25) TABLE-US-00004 TABLE 4 Exposure dose in J/cm.sup.2 to obtain creep time 15 sec for LLDPE irradiated films containing photo-initiator according to Formula (II) and for comparative photo-initiators. UV-treatment was applied on line on primary tube before orientation to obtain 20 micron thick film. Concentration of Exposure Dose*, Number Sample name photo-initiator, % J/cm.sup.2 1 According to Formula (I), 0.35 4.0 R.sub.1 = —O—CH.sub.2—CH.sub.3, R.sub.2 = O—(CH.sub.2).sub.11—CH.sub.3, R.sub.3 = H 2 According to Formula (I), 0.35 3.8 R.sub.1 = —O—CH.sub.2—CO—O—CH.sub.2—CH.sub.3, R.sub.2 = —O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 3 4-octyloxybenzophenone, 0.35 5.0 CAS#1843-05-6 (Comparative) 4 4-hydroxybenzophenone laurate, 0.4 5.5 CAS#35820-92-9, (Comparative) *Exposure dose of UV-irradiation to get 15 sec creep time, 135° C., 57 g load.

(26) It is clear from Table 4, that photo-curing based on photoinitiators of Formula (I) and (II) proved to be more effective as compared to compositions based on comparative photoinitiators.

(27) In Table 5 data is presented on exposure dose needed to achieve 65% gel fraction in samples made of different polyethylenes and of different thickness.

(28) TABLE-US-00005 TABLE 5 Exposure doses (J/cm.sup.2) needed to obtain 65% gel fraction in different samples of polyethylenes of different thickness. Promoter Concentration Expos. Dose*, Number Sample name Thickness (mm) Conc. of PI, % (TMPTMA), % J/cm.sup.2 1 According to Formula (I), 1 1.0 1.0 45 R.sub.1 = —O—CH.sub.2—CH.sub.3, R.sub.2 = O—(CH.sub.2).sub.11—CH.sub.3, R.sub.3 = H 2 According to Formula (I), 2 1.0 1.0 102 R.sub.1 = —O—CH.sub.2—CH.sub.3, R.sub.2 = O—(CH.sub.2).sub.11—CH.sub.3, R.sub.3 = H 3 According to Formula (I), 2 1.0 1.0 45 R.sub.1 = —O—CH.sub.2—CO—O—CH.sub.2—CH.sub.3, R.sub.2 = —O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 4 According to Formula (I), 3 1.0 1.0 100 R.sub.1 = —O—CH.sub.2—CO—O—CH.sub.2—CH.sub.3, R.sub.2 = —O—(CH.sub.2).sub.7—CH.sub.3, R.sub.3 = H 5 4-octyloxybenzophenone 1.0 1.2 1.2 60 CAS#1843-05-6 (Comparative) 6 4-octyloxybenzophenone 2.0 1.3 1.3 145 CAS#1843-05-6 (Comparative) 7 4-hydroxybenzophenone laurate, 1.0 1.0 1.0 78 CAS#35820-92-9, (Comparative) 8 4-hydroxybenzophenone laurate, 3.0 1.3 1.3 168 CAS#35820-92-9, (Comparative)

(29) Data in Table 5 shows that compositions based on photoinitiators of Formula (I) and (II) are substantially more effective than those used in the comparative samples.