Study of Compatibility and Miscibility for Polymers and Copolymers Based on Butadiene and Isoprene

A series of solution blends at different compositions were prepared to determine the compatibility and miscibility of polymers and copolymers based on butadiene and isoprene.  The four controls include 3,4 tapered polyisoprene (PI), 50/50 tapered isoprene-butadiene rubber (IBR), 50% medium vinyl polybutadiene  (MvPBd), and 80% high vinyl polybutadiene (HvPBd). Five blends containing MvPBd (60% Vinyl) and 3,4-PI (78% 3,4 unites) at 10/90, 30/70, 50/50, 70/30, and 90/10 respectively and five blends of HvPBd and 3,4 PI with the same ratios were prepared.  When MvPBd was added to 3,4-PI, two distinct glass transition temperatures were observed, meaning that they are immiscible. With the given data, TGA showed that medium vinyl does not stabilize 3,4-PI. TEM analysis demonstrated that a two phase morphology is clearly observed for blends containing 30% and 50% 3,4-PI.  TEM also showed that there is a small domain and two phase morphology was observed. A single Tg was observed by DSC, suggesting compatibility between HvPBd and 3,4-PI. A broad, single peak was observed in the DMA test revealing that HvPBd and 3,4-PI are highly compatible, while the TGA surprisingly revealed that HvPBd stabilizes 3,4-PI and acts as a radical trap, preventing the decomposition of 3,4-PI. With the addition of IBR to 3,4-PI, the data surprisingly showed that they are compatible.  The TGA showed that thermal stability is improved at high amounts of IBR. As a result of the small temperature difference in HvPBd and IBR, only one Tg is observed in both the DMA and DSC tests.  TEM confirmed that there may be some miscible areas or “phase mixing.”  The TGA showed that IBR slightly improves the thermal stability of IBR.