Block
copolymers consisting of a polyethylene block and a polar
polymer block are interesting structures for the compatibilization
of polyethylene/polar polymer blends or polyethylene-based composites.
Since the synthesis of polyethylene-based block copolymers is an elaborate
process, diblock copolymers consisting of “polyethylene-like”
poly(pentadecalactone) (PPDL) and poly(l-lactide) (PLLA)
were synthesized using a one-pot, sequential-feed ring-opening polymerization
of pentadecalactone (PDL) and l-lactide (LLA). The peculiar
activity of the used aluminum salen catalysts yielded a block copolymer
consisting of two blocks with both a high dispersity, as a result
of intrablock transesterification. Interestingly, interblock transesterification was effectively suppressed.
The obtained poly(PDL-block-LLA) of various block
lengths showed coincidental crystallization of the two blocks with
an associated microphase-separated morphology, in which PLLA spheres
with a high dispersity are distributed within the PPDL matrix. The
complex morphologies is believed to arise from the presence of a whole
range of block sizes as a consequence of the large dispersity of both
blocks. The application of these block copolymers as compatibilizers
for high density polyethylene (HDPE)/PLLA blends led to a clear change
in blend morphology and a steep decrease in particle size of the dispersed
phase. Furthermore, addition of the block copolymers to blends of
linear low density polyethylene (LLDPE) and PLLA led to a significant
increase in adhesion between the two phases. For both HDPE/PLLA and
LLDPE/PLLA blends, the compatibilization efficiency of the poly(PDL-block-LLA) increased when the length of the PPDL block was
increased. The presented results clearly show that PPDL can function
as a substituent for various types of polyethylene, which opens up
a new method for compatibilizing polyethylene with polar polymers
using easy attainable “PE-like” block copolymers.