Synthesis and Characterization of Long Chain Branched Isotactic Polypropylene via a Metallocene Catalyst and T-Reagent
Open Access
Author:
Langston, Justin A
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 02, 2007
Committee Members:
Tze Chiang Chung, Committee Chair/Co-Chair Ralph H Colby, Committee Member Ronald Hedden, Committee Member Ayusman Sen, Committee Member
Keywords:
polypropylene branched branching gel permeation chromatography rheology
Abstract:
Long chain branched isotactic polypropylene (LCBPP) was synthesized via the combination of a metallocene catalyst, p-(3-butenyl)styrene (T-reagent), and hydrogen. T-reagent, in the presence of hydrogen, simultaneously served as comonomer and chain transfer agent, resulting in a high molecular weight, branched polypropylene. The preparation of LCBPP by the addition of T-reagent was a one-step procedure in which the metallocene catalyst remained highly reactive. To understand the structure-property relationships, a series of LCBPP was prepared with similar weight-average molecular weights of about 250,000 g/mol and branch densities ranging from 0 (linear iPP) to 3.3 branches per 10,000 carbon. SEC equipped with triple detectors revealed the presence of high molecular weight branches whose density depended on the concentration of T-reagent, hydrogen, and propylene. Melt properties were examined by small amplitude oscillatory shear and extensional flow measurements. The zero-shear viscosities of LCBPP displayed a systematic increase as branch density increased despite similar molecular weights. Strain hardening was observed in extensional flow of LCBPP. Because of these melt properties, the LCBPP and other branched polypropylenes displayed the ability to retain orientation after high temperature (T > Tm) deformations.
