Metal alkyl borohydrides are used as initiators of polymerisation, particularly in
adhesive compositions for bonding a wide range of substrates including low
surface energy substrates such as polyolefins. As described, the
metal alkyl borohydrides are of the formula I or II. whereinR1 is C1-C10
alkyl,R2 and R3, which may be the same or different, are H, D, C1-C10 alkyl or C3-C10 cycloalkyl, phenyl, or phenyl-substituted C1-C10 alkyl or C3-C10 cycloalkyl, provided that any two of R1-R3 may optionally be part of a carbocyclic ring, andM+ is a
metal ion.In particular,
alkali metal trialkyl borohydrides are used, the
alkali metal salt being selected from:
Lithium triethylborohydride,
Sodium triethylborohydride,
Potassium triethylborohydride,
Lithium tri-sec-butylborohydride,
Sodium tri-sec-butylborohydride,
Potassium tri-sec-butylborohydride, and
Lithium triethylborodeuteride. Other exemplified compounds which are less effective on low
surface energy substrates include Lithium 9-borabicyclo [3.3.1]-
nonane (9BBN)
hydride, Lithium thexylborohydride, Lithium trisiamylborohydride and
Potassium trisiamylborohydride.