In various embodiments, the present invention provides a strong, synthetic elastomer materials (and related methods for making same) with mechanical properties that are controlled by the stereochemically-defined double bonds within their backbone, yet have physical properties that are derived from monomer selection and defined, modifiable, chain end groups. The use of the organocatalyzed, stereospecific addition of thiols to activated alkynes, affords isolated high molar mass materials (>100 kDa) via step-growth polymerization with high levels of cis- or trans-double bond content. Furthermore, in various aspects of the present invention, it has been found that changing the monomer composition and chain end groups provides additional control over the materials' physical properties to provide more efficient compounding with polar additives. Using this approach to elastomer synthesis, further end group modification and toughening through various vulcanization strategies are also possible.

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition.

(X.sub.1).sub.aSi(X.sub.2).sub.4-a,[Formula 1]

In Formula 1, a, X.sub.1, and X.sub.2 are the same as defined in the disclosure.

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition.

(X.sub.1).sub.aN(X.sub.2).sub.3-a[Formula 1]

In Formula 1, a, X.sub.1, and X.sub.2 are the same as defined in the disclosure.

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition.

(X.sub.1).sub.aN(X.sub.2).sub.3-a[Formula 1]

In Formula 1, a, X.sub.1, and X.sub.2 are the same as defined in the disclosure.

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition.

(X.sub.1).sub.a-M.sub.1-([Y-M.sub.2-(X.sub.2).sub.n-1]).sub.m-a[Formula 1]

In Formula 1, a, m, n, M.sub.1, M.sub.2, X.sub.1, X.sub.2 and Y are the same as defined in the disclosure.

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition.

(X.sub.1).sub.aSn(X.sub.2).sub.4-a,[Formula 1]

In Formula 1, a, X.sub.1, and X.sub.2 are the same as defined in the disclosure.

Compositions useful in propylene polymerization catalysts, and in particular solid, hydrocarbon-insoluble, catalyst compositions containing magnesium, titanium, and halogen and further comprising a modifier compound with structure (1):

##STR00001## wherein Q1 is an oxygen containing group selected from CH.sub.2OR.sup.1, C(O)R.sup.1 and C(O)OR.sup.1 and Q2 is selected from R.sup.2 and OR.sup.2; R.sup.1 to R.sup.5 each being independently selected from H, alkyl, aryl, allyl, alkaryl, arylalkyl groups, optionally comprising one or more heteroatoms.

Provided are a method for preparing a polymer composition by using a compound containing a t-butylphenol group, being capable of preventing a yellowing phenomenon of a branched conjugated diene-based polymer with improved branching, and a polymer composition prepared thereby.